The present disclosure relates to sensing circuits, and more particularly, to a multi-touch sensing circuit for minimizing effects of an external capacitive load (C/L).
Touch sensing technology includes a self capacitive method and a mutual capacitive method. Multi-touch is an act of touching at least two objects on a touch portion of a touch sensing device. Pseudo multi-touch is used in the self capacitive method, and multi-touch all point, where any number of independent areas on a touch screen are simultaneously interpreted, is used in the mutual capacitive method.
In the mutual capacitive method, a pulse voltage is applied to a first node of two nodes having constant capacitances, and charge corresponding to the pulse voltage is collected at a second node of the two nodes having constant capacitances. In this case, when a user's finger is put between the two nodes, an electric field between the two nodes is varied, and the amount of charge collected at the second node varies due to the varied electric field. In this case, touch sensing is determined by a difference between the amount of charge collected when touch did not occur and the amount of charge collected when touch occurred.
In the mutual capacitive method, when a large capacitance load exists in a lower portion of a touch sensing circuit, the touch sensing circuit may malfunction. Thus, a shield is typically added to cut off the capacitance load from the touch sensing circuit. However, adding of the shield causes an increase in manufacturing costs of a multi-touch sensing circuit.